I am considering using UnicodeString in threaded program so thread safety comes to mind.
Let's suppose you have a structure like this:
{code}
struct TTaskListEntry
{

John wrote:
  (snip)

UnicodeString reference counting will work just fine. You don't have to
  worry about protecting it.
  (snip)

When you access a UnicodeString via a 'const' reference, the UnicodeString's
  reference count is not incremented. That much is true. But its data payload

(snip)

Does this mean that reference counting increase/decrease is thread-safe (or perhaps atomic operation?) even though the actual UnicodeString data payload management isn't?
    I did test accessing data from 2 threads when it was being written from one and read from another and I do get access violation so it doesn't seem thread safe, and it is kind of odd to me that reference counting is exception to that. And does this depend on version of C++ Builder (I use 2010 version)?
    
    
    

John wrote:
      (snip)

Yes. String reference counts are protected by the RTL itself using its own
      locks.
      (snip)
Only one thread can create a new string payload, and it is initialized with
      a reference count of 1. Only one thread can decrement the reference count

OK here is some example code. It is actually "out of memory" and "invalid pointer operation".
        The example below works without errors (when Button1 is clicked that is). But if you don't wrap shared variable (SupposedToBeThreadSafe) in ProtectWrite and ProtectRead functions (as in commented lines) you should get errors above.
        {code}
        //---------------------------------------------------------------------------
        #include

John wrote:
          (snip)

Assigning a string to another string is thread-safe. Concatenating a string
          to another string is not. Concatenation requires multiple steps (reading
          string lengths, allocating memory, copying string characters), and the strings
          being concatenated could be modified by another thread while the concatenation

OK, thanks. Great answers, as usual!